The yellow fever mosquito, Aedes aegypti, is a prolific vector of human disease. Our long-term goal is to develop new methods for controlling arthropod-borne viruses based on understanding at the molecular level the virus-vector interactions occurring in the mosquito. It has been well demonstrated that arthropod-borne viruses are susceptible to the RNAi responses found in mosquitoes. Thus, RNA interference (RNAi) may play a role in several potential barriers to pathogen transmission present within the vector mosquito. The HYPOTHESIS to be evaluated is that arthropod-borne viruses have evolved to encode suppressors of the RNAi response within their genomes. The specific aims of this proposal are to: (1) Use stable germline transformation to establish and validate an Ae. aegypti "RNAi sensor" strain. (2) Use the sensor strain generated to assay candidate arthropod-borne viruses for the presence of silencing suppressors. Completion of these aims will also generate a novel assay system for the study virus-vector interactions, mosquito genetics, and virus genetics. The total morbidity, mortality, and economic loss associated with diseases caused by mosquito-borne viruses are inestimable. Evidence indicates that RNA silencing may represent a general constraint to the accumulation of virus in the mosquito. The identification of suppressors of RNA silencing encoded in mosquito-borne virus genomes would have enormous implications for understanding the transmission of arthropod-borne viral diseases. [unreadable] [unreadable] [unreadable]